The present invention relates to a technology which improves a spatial resolution in radiation tomography.
It is known that it is possible to improve a spatial resolution in radiation tomography by partially covering an aperture portion formed by collimators provided in a radiation detector with a shield etc. to narrow the aperture. Specifically, in order to achieve it, there is proposed a method to so dispose a “diaphragm” on a surface of the radiation detector as to cover edge portions of detecting elements (see Japanese Patent Application Laid-Open No. 2005-526967, Abstract). This “diaphragm” is constituted by combining strip-like pieces extending in a spreading direction of radiation emitted from a radiation source and in a rotary axis direction (z direction) of the radiation source.
If detection surfaces of detecting elements which constitute a radiation detector are covered partially, a spatial resolution will improve, but the use efficiency of radiation falls that much. Therefore, in radiation tomography, it is not desirable in terms of exposure to radiation to maintain a high spatial resolution using this technique. Therefore, in reality, the spatial resolution may be improved by this method only when a higher spatial resolution is necessary even if it sacrifices radiation use efficiency and, in other cases, radiographs may be taken in a normal state. That is, a method of attaching and detaching a “diaphragm” as required is conceivable.
However, in order to attach and detach the “diaphragm” constituted by combining the above strip-like pieces, it requires a large-scale and complicated attach/detach mechanism, being disadvantageous in terms of cost and space. Further, it is not easy to perform precise alignment. Therefore, the method of attaching and detaching the “diaphragm” is not suitable for changing the spatial resolution in radiation tomography.
Under these circumstances, there is called for a technology which makes it possible to switch a spatial resolution in radiation tomography with a simple structure.